This project will focus mainly on the physiological functions of neuropeptides in the visual system and the relationships and interactions between neuropeptides and other putative neurotransmitter systems. The first step of the study is to figure out which peptides, such as enkephalins, substance P, somatostatin, VIP and TRH are present and their content in the retinas of chick, rabbit and guinea pig. This will be performed by radioimmunoassay, enzyme immunoassay or radioreceptor assay. The peptide containing neurons in the retina of these species will be localized immunocytochemically. After their presence have been established, their biosynthesis and release from the retina will be studied. Pulse-labeled and chase technique will be employed for the biosynthesis studies. Radioisotope labeled peptides in the labeled tissue will be extracted from the tissue, partially purified on a gel filtration column (Sephadex G-50) and then further purified on high performance liquid chromatography (HPLC). The eluents from HPLC will be assayed by immunoassay, thin layer chromatography and the receptor binding studies. The labeled tissue also will be used to study the release of peptides under light stimulus and high K+ depolarization. The effect of divalent ions such as Ca+2 and Co+2 on the peptide release also will be studied. The peptide content and the rate of peptide synthesis in the retina under light and dark adaptation also will be studied. This study will provide the information whether they are involved in the information transmission. The relation of peptidergic system with other transmitter systems will be studied by (a) the effect of peptides on the release and uptake of other transmitters; (b) the effect of other putative transmitters on the release of peptides (c) using double staining techniques to study their relationships. The mechanisms involved in these interactions, particularly the interaction of biogenic amines, peptides and cyclic nucleotides, will be studied. Finally the development of neuropeptide --- the biosynthesis, release and postsynaptic receptors, in the tissue will be studied by the pulse-labeled and chase technique and the receptor binding assay. Consequently, the biochemical changes can be correlated with morphological development.